Thank you all.
Helly, that's a fascinating, if slightly perturbing reply! I know (via treadmil and scanner investigation) that I have an irregular heartbeat and low blood pressure. But the specialist who dealt with me (a couple of years ago) seemed to think that the low BP and bradycardia (which I also have) were consistent with a lifetime of vigorous exercise and that I had nothing to worry about. He also didn't seem concerned about the missed beats. That said, I definitely felt stressed as my hands thawed out, so I can imagine my heart wasn't enjoying the experience. However, I didn't become light-headed and I really was "back to normal" as soon as the nausea abated, which, like the sweat, only lasted a couple of minutes. I think an obvious precaution is just to stop my hands getting that cold in future by assuming they are colder than I think (when they are numb, they are numb!). But I will have a word with my GP.
Edit to add :-
As to the worst pain ever, I support Newcastle United, so probably "no". Seriously, it was bad but I don't think it was as bad as the pain from sequestrated herniated disc - or dentistry as a teenager. But that may be because I knew the pain in my hands was temporary, I don't know.
Thanks
Peter
PS Kim, I really hope you don't get the IBS attacks very often!